3. The spirit column is sometimes much separated by jolting in travelling. If the instrument is in such a condition when received, it should be held by the right hand, bulb downward, and the frame tapped smartly, but cautiously, against the palm of the left hand. The broken thread of spirit will soon begin to join, and by continuing the operation a sufficient time all the bubbles will disappear, and the thermometer become as good as ever. =74. Horticultural Minimum Thermometer.=--This instrument, represented in fig. 56, is a special construction of Rutherford's minimum thermometer to meet the requirements of horticulturists. It is desirable, if not essential, that gardeners should have the means of ascertaining to what temperature stoves and greenhouses descend on cold nights, especially in winter. This thermometer is mounted on a strong cast zinc frame, with the divisions and figures of the scale raised. [Illustration: Fig. 56.] The sunk surface of the frame is painted dark; the figures and division a bright colour, so that observations can be made without a close inspection of the instrument. The directions for using are the same as those given in the preceding section. It may be used as an ordinary thermometer, by simply hanging it from the top loop, in which position, the coloured liquid will always indicate the present temperature. It was a source of annoyance with the ordinary boxwood and flat metal scales, that after a time, exposure to a damp warm atmosphere favoured the growth of confervae upon them, and obliterated the divisions; the plan of raising the figures and divisions of the scale has been found to prevent the destruction of the instrument in this way.